1. Field of the Invention
The present invention relates to an apparatus for coating a photoresist, and more particularly, to a slit coater having a slot nozzle.
2. Description of the Related Art
In a process of fabricating a liquid crystal display device or a semiconductor device, a plurality of photolithographic processes including a exposure process are performed. For the exposure process, a photoresist is applied as a photosensitive material on a substrate. The exposure process may be performed by sequential steps of coating the photoresist on a substrate or a wafer and exposing the photoresist using a mask having a predetermined pattern.
In the exposure process, a photoresist of a predetermined viscosity is applied to the substrate or the like using a coater, such as a spin coater or a spinner. However, the spin coating method using a spin coater is not suitable for applying the photoresist to a large substrate, such as a liquid crystal display panel, and also is uneconomical since an excessive amount of photoresist is consumed during spin coating.
The spin coating method uses centrifugal forces to coat the photoresist evenly. The method may comprise the steps of dropping a predetermined amount of photoresist onto a substrate loaded on a spinner, and uniformly applying the photoresist using the centrifugal force due to high-speed rotation of the spinner.
When the spinner rotates, the photoresist dropped on the spinner is uniformly coated on the substrate, but a considerable amount of photoresist is also scattered off of the spinner. Specifically, the amount of wasted photoresist is much greater than the amount of photoresist coated on the substrate. Furthermore, photoresist fragments scattered during spin coating form particles that may become an environment polluter in a clean room environment.
To solve such problems, a slit coating method using a slit type application nozzle has been proposed. The slit coating method is commonly called a spinless coater because a spinner is not used. Moreover, the slit coater is particularly suitable for applying the photoresist to a large liquid crystal display device.
The slit coater is an apparatus for coating a photoresist onto a glass substrate or the like through a line-type long slit nozzle. Here, the slit nozzle has a bar type nozzle having an ejector on a tip of the nozzle. The photoresist is ejected by the ejector on the tip of the nozzle. The slit nozzle moves from one side of the substrate to the other side, thereby uniformly applying the photoresist onto the substrate.
A general structure of a slit coater will now be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view of a slit coater according to the related art, and FIG. 2 is a sectional view of a photoresist being dropped onto a substrate by the slit coater of FIG. 1.
In FIG. 1, the slit coater in accordance with the related art includes a slit nozzle 101 for applying a photoresist to a substrate 102, a pair of nozzle driving units 103 moving the slit nozzle in one direction, and a photoresist supplying line 106. The slit nozzle 101 is a long bar-shaped nozzle and has a fine slit-shaped injector at a central portion of its lower end adjacent to the substrate 102. A certain amount of photoresist is applied through the injector.
FIG. 2 is a view showing the slit nozzle 101 and the substrate 102. In FIG. 2, the slit nozzle 101 applies the photoresist to the substrate 102 moving from one side of the substrate to the other one side at a constant speed.
The slit coater is advantageous in that the amount of photoresist discarded can be reduced since a photoresist is uniformly applied to the substrate through a fine slit. Here, to apply the photoresist to the substrate with a uniform thickness, a very fine ejector of the slit nozzle is required. For this reason, forming a fine ejector is a core technology in manufacturing a slit coater. Furthermore, to uniformly apply the photoresist onto the substrate, a photoresist supply unit should supply a high quality photoresist without bubbles or particles to the slit nozzle.